This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A345419 #11 Jul 01 2021 23:40:47 %S A345419 1,0,2,-2,4,-4,6,-6,8,10,-10,-12,14,-14,16,18,20,-20,-22,24,-24,-26, %T A345419 28,30,-32,34,-34,36,-36,38,-42,44,46,-46,50,-50,-52,-54,56,58,60,-60, %U A345419 64,-64,66,-66,-70,-74,76,-76,78,80,-80,84,86,88,90,-90,-92,94,-94,98,-102,104,-104 %N A345419 Row 2 of array in A345417. %o A345419 (Python) %o A345419 from sympy.core.numbers import igcdex %o A345419 from sympy import prime %o A345419 def A345419(n): return igcdex(3, prime(n))[0] # _Chai Wah Wu_, Jul 01 2021 %Y A345419 Cf. A345417-A345422. %K A345419 sign %O A345419 1,3 %A A345419 _N. J. A. Sloane_, Jun 19 2021